Boy it's nice being able to just slap a belt on my VW diesels once or twice a year and never worry about any of this junk...

;)

So you don't worry about that 83 300DT with 241k on the clock. I notice you are sticking with this thread til page5.:D

Actually I need to update it again, rolled over 260K last night. And it'll hold till I have the time to replace the chain, or it will not. One of the two. I don't neglect things on purpose, but I am am a bit of a fatilist. My 78 Lincoln was just peachy with that mileage on an old crudy detroit steel chain, surly the MB can hold out awhile longer. I'm still getting over the fact that I have to remember to adjust the valves.


For the record I'd replace the chains and guides, all of them, including the one's nobody ever replaces, and the sprokets, and the oil pump's chain, every 200K or so on something I wanted to keep. Especialy when it's like most of ours are, relativly unknown history, no matter what the papers say.

"but the offset key correction is only allowed up to 3 degrees."

Where in the world did you get that impression?
Why do they make offsets of up to 10 degrees ?

Zen and the art of preventative maintenance...

I would replace the oil pump if you go that deep....

And I'd be forced to pull a rod and/or bearing cap and observe.
I get caught up in things, part of why I don't get started on them till I truly have time. I could just roll a chain in some weekend right now, but it'd bug the heck out of me with the half-assedness feeling of leaving all those guides and worn sprockets.
That's just me though.

My friend's 617 has never had the head off, AFAIK. The other one (on this forum somewhere) - I honestly can't remember, but I don't think there was any head work involved. All the 60x engines I know (admittedly, only a few) returned to zero with a new chain.

The offset correct up to 3 is for the 60x engines, but those you can't adjust - just let it go until 3 or 4 (depending on which TSB you feel like believing at the time), then replace the chain. As to the 61x, the fact that MB allowed 10 degree keys to be produced seems to indicate that up to 10 is acceptable, although I personally would NOT want to do that on MY car...! :eek: New chains just aren't that expensive.

You can tell a lot by looking at the cam sprocket and upper guides. If they are OK, the lower stuff is very likely OK as well. If the top end stuff looks bad, then I'd replace the bottom (or sell the car!). The sprockets don't normally wear or require replacement unless the car had been abused in the past, usually due to infrequent oil change intervals (IMO). I considered replacing my cam sprocket for the hellofit but after seeing the cost, and noting that my old one didn't show a bit of wear, AND the timing went back to zero with a new chain, I promptly forgot about it.

:)

Chain wear is easily and reliably determined by measuring chain stretch since chains tend to wear evenly at every link. There is the more complicated way of checking chain stretch in the engine manual but the simple way which I've described / linked to will catch anything that's seriously wrong and give you a gauge for how fast your chain is wearing based on your driving and maintenance practices. Timing chains can last more than half a million miles and they can fail in less than 50kmi! They need to be checked and Mercedes has provided a simple way to check them.(http://www.meimann.com/docs/mercedes/OM60x_Timing_Chain_TSB.pdf). Just substitute 4 degrees stretch for OM60x's and 5 for OM61x's for recommended replacement.

The TSB is the first time Mercedes spelled it all out CLEARLY in print. This technique is accurate to about 1 degree so if you measure it 3 or 4 times and you get the same number +/- 1 degree or so - you're FINE. There's no need for it to be any more complicated.

Offset keys are available for the OM61x's but MB diesels (unlike gasoline engines) are quite insensitive to small differences in cam timing. If the inj. pump is set correctly, then chain stretch (up to the 4-5 deg limit where MOST mechanics that know their business will suggest that the chain be replaced) will have only little if at all detectable performance effect.

The chain should be tight even if the chain were stretched out to 10 degrees - ALMOST to breaking. You can't tell the wear on a chain on just how it looks, feels, how much mileage is on it or how old it is. You HAVE to measure it, how you do it is up to you.

Finally, a mechanic who says that to measure a chain you have compare it with a new one or has any other bogus excuses (the chain is tight it's still good or it has over 100k on it you should replace it) is IGNORANT, should know better and should not be believed.

Chris

Chris, Finally a paragraph I can agree with... your last one...with regards to the 617 engine... because as long as the offset keys are used to set the valve timing correctly, and the IP is set properly ( and the stretch is not so great that the ratcheting tensioner can not take up the slack ) then the engine does not know or care how long the chain is pin to pin... or by extrapolation... the sum of the pin to pin distances....

Steve Brotherton ( and others including the manual ) have stated that the correct way to measure the chain stretch is by the measurement of number one intake valve movement from the head.....

The manual says ' if there is a performance complaint then this method must be used'....

They make the offset keys in approx 2.5 degree increments... I suggest that they think you should use the keys to keep your engine valves set to that tolerance.... doesn't that make sense ?

And where you got the impression that because a chain has stretched past the limit of the adjustments capable of being taken up by the design of the engine it is close to breaking I don't know...

I used my chainsaw to help a neighbor cut a stump out of the ground last week.... I wound up putting it into the dirt and the burned charcoal from his failed attempt to deal with it.... the chain had no more than 20 minutes work on it... however, I had to take it and get a link taken out of it... however, it was not weaker than a new one.. it had just worn enough that my adjuster on the saw blade could not take up the difference...

CHRIS, WHY DO YOU CONTINUE TO POST A REFERENCE TO A 60x ENGINE WHEN WE ARE TALKING ABOUT A 1984 300SD (617) ?

The procedure outlined for checking chain stretch in the TSB is the same for booth 60x and 61x engines.

There is little danger of the chain failing on OM61x engines until stretch exceeds almost 10 degrees, however I feel 5 degrees should be used as the wear limit (to be on the safe side) and a new chain should be installed since both valve timing (modified using an offset Woodruff key) and pump timing need to be reset once stretch exceeds about 5 degrees so the engine can run efficiently with full power and that is almost as much work as putting in a new chain.

Chris

"The TSB procedure is the same for booth 60x and 61x engines."

Why did they say it applies to 602, 603 and 606 engine numbers...

BUT FAIL TO MENTION THE 617..... ?

IF , in fact, IT IS SUPPOSED TO APPLY TO IT ALSO ?

We are not really talking about chains failing.... you have supplied this as a diversionary point to keep from addressing the fact that the factory supplies the offset cam keys in four sizes to correct for up to 10 degrees of chain elongation...

I suggest there is planning to MB's production of offset keys in those sizes... that they perform exactly as the Factory Shop manual says they should.... and that everyone should consult and read the 617 turbo MB factory shop manual to obtain proper guidance in these procedures..

And that if the MB Engineers wanted something to apply to an engine type.... they would state that in the literature....

If you bring the engine back to specs for the valves with the offset keys.... set the IP..... then you have everything in spec... the FSM does not say a certain amount of miles for replacement ... they know how strong a double roller chain is... they specifically to replace the chain when it can no longer be brought into specs with the offset keys which they supply... the IP can be set in relation to the crank no matter what the chain elongation situation due to internal design.... not so with the cam sprocket... thus the need for the offset keys....

Leathermang,

You are making assumptions and not reading the manual verbatim. No where in the OM617 manual does it say install offset keys until they can't bring timing back to specs. Two statements are made. Statement #1 says you can use an offset key to bring timing to specs which are 11.5 degrees for a new chain and 13.5 degrees for a used chain as stated on the specs page of the procedure. If specs for a used chain can't be met, a new chain is in order. Statement #2 says keys are available in these sizes, but it doesn't say you can use them to correct chain stretch until you run out of keys.

The 10 deg key is to be used when much material has been removed from the head and cam timing would be very late. Remember as I said these keys were not designed just for the OM617 engine. They have been around for about 40 years. In the old days if you overheated and warped a 4 or 6 aluminum cylinder head, you put it into a machinist's oven overnight and straightened it to within .004 of an inch. Then you stripped both sides of the head and machined both sides to be flat and parallel so the gasket would hold on one side of the head and the cam would turn freely on the other side. Now your timing could be off a bunch so you could measure it with a dial indicator and make the adjustment with a combination of one of the keys and rotation of the sprocket one tooth. One tooth on the sprocket equals 18 deg. As I said before MB takes a picture and uses it forever. I'll bet if I look I will find this same type setting about the keys in my old M108 engine manual which goes back to the 60s.

Autozen, you have good points - but where does Mercedes formally state the limit of wear for the 617 chain? With a non-milled head, and old/original chain, if a 10 degree offset key got valve timing back to the allowed 13.5, wouldn't that technically be allowed? (I personally don't think this is very wise, as noted in my previous posts - but MB doesn't seem to have anything in writing to state otherwise.)

:confused:

Gsxr,
On page one of job# 05-215 if I got the job # right. It gives specs of 11.5 for new chain and 13.5 with chain with over 20,000 kilometers. I interpret that to mean if it hasn't stretched more than 2 deg, you don't need to replace the chain. I can't imagine MB saying you should bring a used chain to within 2 deg of new. Also I know it is a different engine, but if you carefully read the TSB chris provided, it says if you measure a chain stretch of more than 9 deg, you should check the pistons for contact with the valves.